Most metals, even marine-grade metals, show evidence of corrosion after use in water environments, including salt, brackish, and fresh water environments. Corrosion is especially pronounced in cold, deep salt water. Over time, the corrosion can be detrimental to long-term operational sustainment of the metal object that is exposed to the water environment.
The use of friction stir welding (FSW) to join two metallic objects at a weld joint is known. When those objects are exposed to a water environment, it has been observed that at the location of the FSW joint, there is little or no corrosion that occurs, while significant corrosion occurs on the metal objects at locations outside of the FSW joint in the base metal alloy.
The use of the FSW process to connect the ends of tubes to a tube sheet in heat exchanger applications are disclosed in U.S. Pat. No. 8,439,250 and in U.S. Published Patent Application No. 2013/0037601. In addition, the formation of a tube using the FSW process is disclosed in U.S. Provisional Application No. 61/777,419, filed on Mar. 12, 2013 and titled Friction Surface Stir Process.